1. Field of the Invention
The present invention relates to a waterproof lens barrel, and in particular it relates to a waterproof lens barrel in which a movable lens barrel which is moved in the optical axis direction includes inner and outer cylinders of which a space defined therebetween is sealed by an annular seal member.
2. Description of the Related Art
In a drip-proof/waterproof lens barrel which has been developed by the assignee of the present application, a movable barrel of a water tight structure is composed of inner and outer cylinders; and a space defined between the inner and outer cylinders is sealed by an annular seal member. Since the outer cylinder is in contact with the seal member, it is preferable that the outer cylinder be a metal pressing, formed from a metal such as an aluminum alloy, to provide increased surface precision and surface hardness. The inner cylinder is preferably made of a synthetic resin mold which can be easily formed to a desired shape. In the simplest seal structure, the annular seal member is held by one of the inner and outer cylinders. However, there is a limitation to the size of the inner and outer cylinders, and hence it is difficult to provide a holding portion to hold the annular seal member (e.g., an O-ring) on the inner cylinder or the outer cylinder. If the annular seal member is held on the outer periphery of the inner cylinder which is fitted inside the outer cylinder, since the insertion resistance increases as the axial fitting length of the inner and outer cylinders increases, it takes a long time to fit the inner cylinder in the outer cylinder, with the annular seal member being incorporated therebetween, and the seal member can be twisted or damaged.